6. Very low level harmonic radiation. 7. Very long life measured in decades. S. Operate at high voltage to reduce power losses in power busses. 9. Ability to interface directly with solar array without any intervening power conditioning. 10. Low emission of X-rays. 11. Ability to withstand bombardment by high energetic particles in space. 12. Low ratio of mass to microwave power output. 13. Low cost. The magnetron whose design and performance is described in Appendix A and in reference [2] can meet all of these requirements simultaneously with the exception of items 1 and 5. The magnetron - for example the microwave oven magnetron - has very low levels of broadband noise at its normal operating efficiencies of from 70% to 75%, but when the magnetic field is increased to obtain higher efficiencies the noise level increases. [2,4] To place this discussion in a larger perfective, the microwave oven magnetron, when operated continuously as it would be in all power beaming applications, has a very high ratio of the power output of the tube at the assigned frequency to any broadband noise, much higher than that observed and reported upon in any other generator. The tube prefers to operate in this quiet mode despite a very wide range of operating parameters and environmental conditions imposed upon the tube. However, there is also a noisy mode of operation that can be avoided, but an understanding of which is highly desirable. Now the problem is that although there is extensive experimental data on this quiet mode of operation, there is no known explanation of why this tube prefers to operate in the quiet mode. The author believes that it is necessary to know why this tube is so quiet, not only to optimize the current design for quiet operation but also for guidance on how to design for low noise at the desired high efficiencies of operation. The author also believes that the best explanation may be obtained by computer simulation of the magnetron operation. There is an ongoing effort to describe the operation of crossed field microwave tubes, particularly as they relate to noise. Currently the Bureau of Ships is supporting efforts to simulate the noise in the crossed field amplifier that is used in the Aegis radar. This program is being managed at SAIC in Washington, D.C. with David Chernin as the director of the program Currently, this program is not being applied to magnetrons but it probably could be because the cross field amplifier and the magnetron are very closely related in their operating principles. Last summer there was an international symposium on crossed field devices held in Ann Arbor Michigan and a Proceedings was published. There were approximately ten papers given on observed phenomena in magnetrons related to noise producing mechanisms, but they did not explain the desire of the microwave oven magnetron to operate in the quiet mode. During the first part of June 1996, the 23rd IEEE International Conference on Plasma Science will be held in Boston, MA At that Conference there will be a special session on “Computer Simulation of Vacuum Power Tubes” at which the writer will challenge the computer experts to explain why the microwave oven magnetron prefers to operate in the “quiet mode.”
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